In the 1780s, Johann Helfrich Müller, a German engineer, was tasked with checking tables of data on the volumes of trees. To make the work go faster, he designed this machine:

Müller's calculating machine is very similar to the machine of Hahn and was based on the Stepped Drum of Leibniz, but it is larger (285 mm diameter, 95 mm height, weight 15.4 kg). It was in the form of a round box with a handle placed centrally and the number wheels concentrically arranged around the handle. It could calculate with 14 figures and its number and gear wheels could be altered to enable it to operate with non-decimal number systems.

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Technically, I think this is a calculator, not a computer. A computer is generally assumed to have branching and looping capability. But this, and the inventor's proposed difference engine to calculate arithmetical progressions and even print out the results as it goes, are truly amazing in their own right.